This invention relates to carpet installations, and in particular to a new and improved heat bond tape for carpet seaming, and a method of manufacture of such tape.
Heat bond tapes have been in use for a considerable period of time, and the typical tape includes a backing strip, typically paper, a reinforcing webbing, typically a yarn, and a thermoplastic adhesive material The adhesive material is heated during the carpet seaming operation and adheres the webbing and backing strip to the back of the edges of the two pieces of carpet being joined.
The backing strip acts as a carrier for the adhesive and the reinforcing fiber or yarn and may be of paper, cloth, plastic, foil, or the like Desirably, the backing strip is made wide enough to prevent adhesive from being squeezed around its edges and sticking to the pad or floor or other material beneath. Also the backing strip is made relatively non-porous to prevent adhesive from flowing through it. Desirably, the backing strip is somewhat extensible in the longitudinal direction of the strip so that the backing strip will not tear when stretched during carpet installation.
Fibers of the reinforcing webbing are positioned transverse to the longitudinal axis of the backing strip and usually are made of fiberglass or other non-extensible yarn to provide lateral strength across the carpet seam. At the same time, the webbing desirably is extensible in the longitudinal direction so that it will not fracture when the heat bond tape is stretched.
In the past, the webbing has been provided in one of three varieties. In one arrangement, the webbing is knitted or woven as a yarn tape which is then glued to the backing strip. In another arrangement, the knitted yarn tape is stitched to the backing strip. This type of construction is shown in U.S Pat. No. 3,485,704. In the third variation, individual fibers are positioned transversely on the backing strip and are glued in place. There are disadvantages to each of these arrangements, and it is an object of the present invention to provide a new and improved heat bond tape which overcomes the disadvantages.
When a heat bond tape is installed, the adhesive material adheres to the back of the carpet edges and to the fiber used in the webbing. When the joined carpet is stretched, a tensile shear stress is produced at the seam and this stress is transferred through the adhesive to the webbing material. Both the adhesive material and the webbing must resist the tensile shear stress in order to maintain the integrity of the seam.
The thermoplastic adhesive material typically includes a polymer for strength and a tackifier for adhesion, along with filler materials and an anti-oxidant for improved aging.
In one arrangement, the webbing is positioned over the paper and the adhesive material in molten state is applied and formed with a flat surface or with parallel rows of beads, as desired. On cooling, the adhesive material holds the webbing and paper together. An advantage of this arrangement is that the adhesive material completely surrounds the fibers of the webbing resulting in a matrix which reduces the natural brittleness of the fibers and provides a flexible high strength reinforcement material. A disadvantage of this arrangement is that the fibers of the webbing can change position and orientation whenever the adhesive is in the molten state. This can occur during assembly when the transverse fibers can become skewed or bowed or other than perpendicular to the longitudinal axis of the tape. Also, when this form of heat bond tape is being used to join carpet edges with the adhesive material again molten, the fibers can become disoriented, and also can stick to the heating iron as it is removed from the tape. When the transverse fibers are not straight and perpendicular to the seam, the resistance of the heat bond tape to the tensile shear stress is substantially reduced, since the seam will separate while the bowed fibers are being straightened and the oblique fibers are being brought perpendicular by the tensile shear stress. This results in an increase of stress on fewer fibers, with fiber breakage and seam opening.
In an alternative construction, the webbing yarns are glued to the backing strip with a first adhesive, prior to applying the thermoplastic adhesive material. This gluing operation effectively fixes the webbing to the paper and substantially eliminates the movement of the yarn during manufacture and during application to the carpet. However since the fibers are fixed to the backing strip by an adhesive, the subsequently applied thermoplastic adhesive material is prevented from completely surrounding the fibers in the manner as previously described where the thermoplastic adhesive material is utilized for bonding the webbing to the backing strip. In this type of construction, the fibers are not completely surrounded by the adhesive material resulting in a tape that is less strong and more brittle than the previously described tape.
In a variation of such construction, individual fibers are glued directly to the backing strip, usually both in transverse and longitudinal directions. After this gluing operation, the thermoplastic material is applied in the conventional manner. This design eliminates the knitting operation for the webbing but does prevent the thermoplastic adhesive material from surrounding the fibers. In another variation, the webbing, typically a previously knitted or woven yarn tape, is glued directly onto the paper backing strip. After this gluing operation, the thermoplastic material is applied in the conventional manner.
In another arrangement, the webbing, typically a knitted yarn tape, is stitched directly onto the paper backing strip during the knitting operation. With this arrangement, the webbing is maintained in position during application of the thermoplastic material and during carpet seaming. However the holes in the backing strip resulting from the stitching operation permit flow of the molten adhesive through the backing strip. This is a problem during manufacture and also during installation with the heat bond tape becoming attached to the underlying pad or floor.